Method for adaptation parameter set reference and constraints in coded video stream

ABSTRACT

A method of decoding an encoded video bitstream using at least one processor, including: obtaining from the encoded video bitstream a coded video sequence including a picture unit corresponding to a coded picture; obtaining a picture header (PH) network abstraction layer (NAL) unit included in the picture unit; obtaining at least one video coding layer (VCL) network abstraction layer (NAL) unit included in the picture unit; decoding the coded picture based on the PH NAL unit, the at least one VCL NAL unit, and an adaptation parameter set (APS) included in an APS NAL unit obtained from the coded video sequence; and outputting the decoded picture, wherein the APS NAL unit is available to the at least one processor before the at least one VCL NAL unit.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.17/733,311 filed Apr. 29, 2022, which is a continuation of U.S.application Ser. No. 17/038,541 filed Sep. 30, 2020, issued as U.S. Pat.No. 11,343,524 on May 24, 2022, which claims priority from 35 U.S.C. §119 to U.S. Provisional Application No. 62/954,096, filed on Dec. 27,2019, in the United States Patent & Trademark Office, the disclosure ofwhich is incorporated herein by reference in its entirety.

FIELD

The disclosed subject matter relates to video coding and decoding, andmore specifically, to adaptation parameter set reference and constraintsin a coded video stream.

BACKGROUND

Video coding and decoding using inter-picture prediction with motioncompensation has been known. Uncompressed digital video can consist of aseries of pictures, each picture having a spatial dimension of, forexample, 1920×1080 luminance samples and associated chrominance samples.The series of pictures can have a fixed or variable picture rate(informally also known as frame rate), of, for example 60 pictures persecond or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GByte of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reducing aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signal is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision contribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding, some of which will be introducedbelow.

Historically, video encoders and decoders tended to operate on a givenpicture size that was, in most cases, defined and stayed constant for acoded video sequence (CVS), Group of Pictures (GOP), or a similarmulti-picture timeframe. For example, in MPEG-2, system designs areknown to change the horizontal resolution (and, thereby, the picturesize) dependent on factors such as activity of the scene, but only at Ipictures, hence typically for a GOP. The resampling of referencepictures for use of different resolutions within a CVS is known, forexample, from ITU-T Rec. H.263 Annex P. However, here the picture sizedoes not change, only the reference pictures are being resampled,resulting potentially in only parts of the picture canvas being used (incase of downsampling), or only parts of the scene being captured (incase of upsampling). Further, H.263 Annex Q allows the resampling of anindividual macroblock by a factor of two (in each dimension), upward ordownward. Again, the picture size remains the same. The size of amacroblock is fixed in H.263, and therefore does not need to besignaled.

SUMMARY

In an embodiment, there is provided a method of decoding an encodedvideo bitstream using at least one processor, including: obtaining fromthe encoded video bitstream a coded video sequence including a pictureunit corresponding to a coded picture; obtaining a picture header (PH)network abstraction layer (NAL) unit included in the picture unit;obtaining at least one video coding layer (VCL) network abstractionlayer (NAL) unit included in the picture unit; decoding the codedpicture based on the PH NAL unit, the at least one VCL NAL unit, and anadaptation parameter set (APS) included in an APS NAL unit obtained fromthe coded video sequence; and outputting the decoded picture, whereinthe APS NAL unit is available to the at least one processor before theat least one VCL NAL unit.

In an embodiment, there is provided a device for decoding an encodedvideo bitstream, including: at least one memory configured to storeprogram code; and at least one processor configured to read the programcode and operate as instructed by the program code, the program codeincluding: first obtaining code configured to cause the at least oneprocessor to obtain from the encoded video bitstream a coded videosequence including a picture unit corresponding to a coded picture;second obtaining code configured to cause the at least one processor toobtain a picture header (PH) network abstraction layer (NAL) unitincluded in the picture unit; third obtaining code configured to causethe at least one processor to obtain at least one video coding layer(VCL) network abstraction layer (NAL) unit included in the picture unit;decoding code configured to cause the at least one processor to decodethe coded picture based on the PH NAL unit, the at least one VCL NALunit, and an adaptation parameter set (APS) included in an APS NAL unitobtained from the coded video sequence; and output code configured tocause the at least one processor to output the decoded picture, whereinthe APS NAL unit is available to the at least one processor before theat least one VCL NAL unit.

In an embodiment, there is provided a non-transitory computer-readablemedium storing instructions, the instructions including: one or moreinstructions that, when executed by one or more processors of a devicefor decoding an encoded video bitstream, cause the one or moreprocessors to: obtain from the encoded video bitstream a coded videosequence including a picture unit corresponding to a coded picture;obtain a picture header (PH) network abstraction layer (NAL) unitincluded in the picture unit; obtain at least one video coding layer(VCL) network abstraction layer (NAL) unit included in the picture unit;decode the coded picture based on the PH NAL unit, the at least one VCLNAL unit, and an adaptation parameter set (APS) included in an APS NALunit obtained from the coded video sequence; and output the decodedpicture, wherein the APS NAL unit is available to the at least oneprocessor before the at least one VCL NAL unit.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIGS. 5A-5E are schematic illustrations of options for signaling ARCparameters in accordance with an embodiment, in accordance with anembodiment.

FIGS. 6A-6B are schematic illustration of examples of syntax tables inaccordance with an embodiment.

FIG. 7 is an example of prediction structure for scalability withadaptive resolution change, in accordance with an embodiment.

FIG. 8 is an example of a syntax table in accordance with an embodiment.

FIG. 9 is a schematic illustration of a simplified block diagram ofparsing and decoding POC cycle per access unit and access unit countvalue, in accordance with an embodiment.

FIG. 10 is a schematic illustration of a video bitstream structureincluding multi-layered sub-pictures, in accordance with an embodiment.

FIG. 11 is a schematic illustration of a display of the selectedsub-picture with an enhanced resolution, in accordance with anembodiment.

FIG. 12 is a block diagram of a decoding and display process for a videobitstream including multi-layered sub-pictures, in accordance with anembodiment.

FIG. 13 is a schematic illustration of 360 video display with anenhancement layer of a sub-picture, in accordance with an embodiment.

FIG. 14 is an example of a layout information of sub-pictures and itscorresponding layer and picture prediction structure, in accordance withan embodiment.

FIG. 15 is an example of a layout information of sub-pictures and itscorresponding layer and picture prediction structure, with spatialscalability modality of local region, in accordance with an embodiment.

FIG. 16 is an example of a syntax table for sub-picture layoutinformation, in accordance with an embodiment.

FIG. 17 is an example of a syntax table of SEI message for sub-picturelayout information, in accordance with an embodiment.

FIG. 18 is an example of a syntax table to indicate output layers andprofile/tier/level information for each output layer set, in accordancewith an embodiment.

FIG. 19 is an example of a syntax table to indicate output layer mode onfor each output layer set, in accordance with an embodiment.

FIG. 20 is an example of a syntax table to indicate the presentsubpicture of each layer for each output layer set, in accordance withan embodiment.

FIG. 21 is a schematic illustration of a bitstream conformancerequirement in accordance with an embodiment.

FIG. 22 is a flowchart of an example process for decoding an encodedvideo bitstream in accordance with an embodiment.

FIG. 23 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION

FIG. 1 illustrates a simplified block diagram of a communication system(100) according to an embodiment of the present disclosure. The system(100) may include at least two terminals (110-120) interconnected via anetwork (150). For unidirectional transmission of data, a first terminal(110) may code video data at a local location for transmission to theother terminal (120) via the network (150). The second terminal (120)may receive the coded video data of the other terminal from the network(150), decode the coded data and display the recovered video data.Unidirectional data transmission may be common in media servingapplications and the like.

FIG. 1 illustrates a second pair of terminals (130, 140) provided tosupport bidirectional transmission of coded video that may occur, forexample, during videoconferencing. For bidirectional transmission ofdata, each terminal (130, 140) may code video data captured at a locallocation for transmission to the other terminal via the network (150).Each terminal (130, 140) also may receive the coded video datatransmitted by the other terminal, may decode the coded data and maydisplay the recovered video data at a local display device.

In FIG. 1 , the terminals (110-140) may be illustrated as servers,personal computers and smart phones but the principles of the presentdisclosure may be not so limited. Embodiments of the present disclosurefind application with laptop computers, tablet computers, media playersand/or dedicated video conferencing equipment. The network (150)represents any number of networks that convey coded video data among theterminals (110-140), including for example wireline and/or wirelesscommunication networks. The communication network (150) may exchangedata in circuit-switched and/or packet-switched channels. Representativenetworks include telecommunications networks, local area networks, widearea networks and/or the Internet. For the purposes of the presentdiscussion, the architecture and topology of the network (150) may beimmaterial to the operation of the present disclosure unless explainedherein below.

FIG. 2 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and decoder in astreaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (213), that caninclude a video source (201), for example a digital camera, creating afor example uncompressed video sample stream (202). That sample stream(202), depicted as a bold line to emphasize a high data volume whencompared to encoded video bitstreams, can be processed by an encoder(203) coupled to the camera (201). The encoder (203) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video bitstream (204), depicted as a thin line toemphasize the lower data volume when compared to the sample stream, canbe stored on a streaming server (205) for future use. One or morestreaming clients (206, 208) can access the streaming server (205) toretrieve copies (207, 209) of the encoded video bitstream (204). Aclient (206) can include a video decoder (210) which decodes theincoming copy of the encoded video bitstream (207) and creates anoutgoing video sample stream (211) that can be rendered on a display(212) or other rendering device (not depicted). In some streamingsystems, the video bitstreams (204, 207, 209) can be encoded accordingto certain video coding/compression standards. Examples of thosestandards include ITU-T Recommendation H.265. Under development is avideo coding standard informally known as Versatile Video Coding or VVC.The disclosed subject matter may be used in the context of VVC.

FIG. 3 may be a functional block diagram of a video decoder (210)according to an embodiment of the present disclosure.

A receiver (310) may receive one or more codec video sequences to bedecoded by the decoder (210); in the same or another embodiment, onecoded video sequence at a time, where the decoding of each coded videosequence is independent from other coded video sequences. The codedvideo sequence may be received from a channel (312), which may be ahardware/software link to a storage device which stores the encodedvideo data. The receiver (310) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (310) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (315) may be coupled inbetween receiver (310) and entropy decoder/parser (320) (“parser”henceforth). When receiver (310) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer (315) may not be needed, or can besmall. For use on best effort packet networks such as the Internet, thebuffer (315) may be required, can be comparatively large and canadvantageously of adaptive size.

The video decoder (210) may include a parser (320) to reconstructsymbols (321) from the entropy coded video sequence. Categories of thosesymbols include information used to manage operation of the decoder(210), and potentially information to control a rendering device such asa display (212) that is not an integral part of the decoder but can becoupled to it, as was shown in FIG. 3 . The control information for therendering device(s) may be in the form of Supplementary EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (320) may parseand/or entropy-decode the coded video sequence received. The coding ofthe coded video sequence can be in accordance with a video codingtechnology or standard, and can follow principles well known to a personskilled in the art, including variable length coding, Huffman coding,arithmetic coding with or without context sensitivity, and so forth. Theparser (320) may extract from the coded video sequence, a set ofsubgroup parameters for at least one of the subgroups of pixels in thevideo decoder, based upon at least one parameter corresponding to thegroup. Subgroups can include Groups of Pictures (GOPs), pictures,sub-pictures, tiles, slices, bricks, macroblocks, Coding Tree Units(CTUs) Coding Units (CUs), blocks, Transform Units (TUs), PredictionUnits (PUs) and so forth. A tile may indicate a rectangular region ofCU/CTUs within a particular tile column and row in a picture. A brickmay indicate a rectangular region of CU/CTU rows within a particulartile. A slice may indicate one or more bricks of a picture, which arecontained in an NAL unit. A sub-picture may indicate an rectangularregion of one or more slices in a picture. The entropy decoder/parsermay also extract from the coded video sequence information such astransform coefficients, quantizer parameter values, motion vectors, andso forth.

The parser (320) may perform entropy decoding and/or parsing operationon the video sequence received from the buffer (315), so to createsymbols (321).

Reconstruction of the symbols (321) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (320). The flow of such subgroup control information between theparser (320) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, decoder 210 can beconceptually subdivided into a number of functional units as describedbelow. In a practical implementation operating under commercialconstraints, many of these units interact closely with each other andcan, at least partly, be integrated into each other. However, for thepurpose of describing the disclosed subject matter, the conceptualsubdivision into the functional units below is appropriate.

A first unit is the scaler and/or inverse transform unit (351). Thescaler and/or inverse transform unit (351) receives quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (321) from the parser (320). It can output blockscomprising sample values, that can be input into aggregator (355).

In some cases, the output samples of the scaler and/or inverse transform(351) can pertain to an intra coded block; that is: a block that is notusing predictive information from previously reconstructed pictures, butcan use predictive information from previously reconstructed parts ofthe current picture. Such predictive information can be provided by anintra picture prediction unit (352). In some cases, the intra pictureprediction unit (352) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current (partly reconstructed) picture(358). The aggregator (355), in some cases, adds, on a per sample basis,the prediction information the intra prediction unit (352) has generatedto the output sample information as provided by the scaler and/orinverse transform unit (351).

In other cases, the output samples of the scaler and/or inversetransform unit (351) can pertain to an inter coded, and potentiallymotion compensated block. In such a case, a Motion CompensationPrediction unit (353) can access reference picture memory (357) to fetchsamples used for prediction. After motion compensating the fetchedsamples in accordance with the symbols (321) pertaining to the block,these samples can be added by the aggregator (355) to the output of thescaler and/or inverse transform unit (in this case called the residualsamples or residual signal) so to generate output sample information.The addresses within the reference picture memory form where the motioncompensation unit fetches prediction samples can be controlled by motionvectors, available to the motion compensation unit in the form ofsymbols (321) that can have, for example X, Y, and reference picturecomponents. Motion compensation also can include interpolation of samplevalues as fetched from the reference picture memory when sub-sampleexact motion vectors are in use, motion vector prediction mechanisms,and so forth.

The output samples of the aggregator (355) can be subject to variousloop filtering techniques in the loop filter unit (356). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video bitstream andmade available to the loop filter unit (356) as symbols (321) from theparser (320), but can also be responsive to meta-information obtainedduring the decoding of previous (in decoding order) parts of the codedpicture or coded video sequence, as well as responsive to previouslyreconstructed and loop-filtered sample values.

The output of the loop filter unit (356) can be a sample stream that canbe output to the render device (212) as well as stored in the referencepicture memory for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. Once a coded picture is fullyreconstructed and the coded picture has been identified as a referencepicture (by, for example, parser (320)), the current reference picture(358) can become part of the reference picture buffer (357), and a freshcurrent picture memory can be reallocated before commencing thereconstruction of the following coded picture.

The video decoder 210 may perform decoding operations according to apredetermined video compression technology that may be documented in astandard, such as ITU-T Rec. H.265. The coded video sequence may conformto a syntax specified by the video compression technology or standardbeing used, in the sense that it adheres to the syntax of the videocompression technology or standard, as specified in the videocompression technology document or standard and specifically in theprofiles document therein. Also necessary for compliance can be that thecomplexity of the coded video sequence is within bounds as defined bythe level of the video compression technology or standard. In somecases, levels restrict the maximum picture size, maximum frame rate,maximum reconstruction sample rate (measured in, for example megasamples per second), maximum reference picture size, and so on. Limitsset by levels can, in some cases, be further restricted throughHypothetical Reference Decoder (HRD) specifications and metadata for HRDbuffer management signaled in the coded video sequence.

In an embodiment, the receiver (310) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (210) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or SNR enhancementlayers, redundant slices, redundant pictures, forward error correctioncodes, and so on.

FIG. 4 may be a functional block diagram of a video encoder (203)according to an embodiment of the present disclosure.

The encoder (203) may receive video samples from a video source (201)(that is not part of the encoder) that may capture video image(s) to becoded by the encoder (203).

The video source (201) may provide the source video sequence to be codedby the encoder (203) in the form of a digital video sample stream thatcan be of any suitable bit depth (for example: 8 bit, 10 bit, 12 bit, .. . ), any color space (for example, BT.601 Y CrCB, RGB, . . . ) and anysuitable sampling structure (for example Y CrCb 4:2:0, Y CrCb 4:4:4). Ina media serving system, the video source (201) may be a storage devicestoring previously prepared video. In a videoconferencing system, thevideo source (203) may be a camera that captures local image informationas a video sequence. Video data may be provided as a plurality ofindividual pictures that impart motion when viewed in sequence. Thepictures themselves may be organized as a spatial array of pixels,wherein each pixel can comprise one or more sample depending on thesampling structure, color space, etc. in use. A person skilled in theart can readily understand the relationship between pixels and samples.The description below focusses on samples.

According to an embodiment, the encoder (203) may code and compress thepictures of the source video sequence into a coded video sequence (443)in real time or under any other time constraints as required by theapplication. Enforcing appropriate coding speed is one function ofController (450). Controller controls other functional units asdescribed below and is functionally coupled to these units. The couplingis not depicted for clarity. Parameters set by controller can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. A person skilled in the art can readily identify other functionsof controller (450) as they may pertain to video encoder (203) optimizedfor a certain system design.

Some video encoders operate in what a person skilled in the are readilyrecognizes as a “coding loop”. As an oversimplified description, acoding loop can consist of the encoding part of an encoder (430)(“source coder” henceforth) (responsible for creating symbols based onan input picture to be coded, and a reference picture(s)), and a (local)decoder (433) embedded in the encoder (203) that reconstructs thesymbols to create the sample data a (remote) decoder also would create(as any compression between symbols and coded video bitstream islossless in the video compression technologies considered in thedisclosed subject matter). That reconstructed sample stream is input tothe reference picture memory (434). As the decoding of a symbol streamleads to bit-exact results independent of decoder location (local orremote), the reference picture buffer content is also bit exact betweenlocal encoder and remote encoder. In other words, the prediction part ofan encoder “sees” as reference picture samples exactly the same samplevalues as a decoder would “see” when using prediction during decoding.This fundamental principle of reference picture synchronicity (andresulting drift, if synchronicity cannot be maintained, for examplebecause of channel errors) is well known to a person skilled in the art.

The operation of the “local” decoder (433) can be the same as of a“remote” decoder (210), which has already been described in detail abovein conjunction with FIG. 3 . Briefly referring also to FIG. 4 , however,as symbols are available and encoding and/or decoding of symbols to acoded video sequence by entropy coder (445) and parser (320) can belossless, the entropy decoding parts of decoder (210), including channel(312), receiver (310), buffer (315), and parser (320) may not be fullyimplemented in local decoder (433).

An observation that can be made at this point is that any decodertechnology except the parsing and/or entropy decoding that is present ina decoder also necessarily needs to be present, in substantiallyidentical functional form, in a corresponding encoder. For this reason,the disclosed subject matter focusses on decoder operation. Thedescription of encoder technologies can be abbreviated as they are theinverse of the comprehensively described decoder technologies. Only incertain areas a more detail description is required and provided below.

As part of its operation, the source coder (430) may perform motioncompensated predictive coding, which codes an input frame predictivelywith reference to one or more previously-coded frames from the videosequence that were designated as “reference frames.” In this manner, thecoding engine (432) codes differences between pixel blocks of an inputframe and pixel blocks of reference frame(s) that may be selected asprediction reference(s) to the input frame.

The local video decoder (433) may decode coded video data of frames thatmay be designated as reference frames, based on symbols created by thesource coder (430). Operations of the coding engine (432) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 4 ), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (433) replicates decodingprocesses that may be performed by the video decoder on reference framesand may cause reconstructed reference frames to be stored in thereference picture cache (434). In this manner, the encoder (203) maystore copies of reconstructed reference frames locally that have commoncontent as the reconstructed reference frames that will be obtained by afar-end video decoder (absent transmission errors).

The predictor (435) may perform prediction searches for the codingengine (432). That is, for a new frame to be coded, the predictor (435)may search the reference picture memory (434) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(435) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (435), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (434).

The controller (450) may manage coding operations of the video coder(430), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (445). The entropy coder translatesthe symbols as generated by the various functional units into a codedvideo sequence, by loss-less compressing the symbols according totechnologies known to a person skilled in the art as, for exampleHuffman coding, variable length coding, arithmetic coding, and so forth.

The transmitter (440) may buffer the coded video sequence(s) as createdby the entropy coder (445) to prepare it for transmission via acommunication channel (460), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(440) may merge coded video data from the video coder (430) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (450) may manage operation of the encoder (203). Duringcoding, the controller (450) may assign to each coded picture a certaincoded picture type, which may affect the coding techniques that may beapplied to the respective picture. For example, pictures often may beassigned as one of the following frame types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other frame in the sequence as a source of prediction.Some video codecs allow for different types of Intra pictures,including, for example Independent Decoder Refresh Pictures. A personskilled in the art is aware of those variants of I pictures and theirrespective applications and features.

A Predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A Bi-directionally Predictive Picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded non-predictively,via spatial prediction or via temporal prediction with reference to onepreviously coded reference pictures. Blocks of B pictures may be codednon-predictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video coder (203) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video coder (203) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (440) may transmit additional datawith the encoded video. The video coder (430) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, Supplementary EnhancementInformation (SEI) messages, Visual Usability Information (VUI) parameterset fragments, and so on.

Recently, compressed domain aggregation or extraction of multiplesemantically independent picture parts into a single video picture hasgained some attention. In particular, in the context of, for example,360 coding or certain surveillance applications, multiple semanticallyindependent source pictures (for examples the six cube surface of acube-projected 360 scene, or individual camera inputs in case of amulti-camera surveillance setup) may require separate adaptiveresolution settings to cope with different per-scene activity at a givenpoint in time. In other words, encoders, at a given point in time, maychoose to use different resampling factors for different semanticallyindependent pictures that make up the whole 360 or surveillance scene.When combined into a single picture, that, in turn, requires thatreference picture resampling is performed, and adaptive resolutioncoding signaling is available, for parts of a coded picture.

Below, a few terms will be introduced that will be referred to in theremainder of this description.

Sub-Picture may refer to a, in some cases, rectangular arrangement ofsamples, blocks, macroblocks, coding units, or similar entities that aresemantically grouped, and that may be independently coded in changedresolution. One or more sub-pictures may form a picture. One or morecoded sub-pictures may form a coded picture. One or more sub-picturesmay be assembled into a picture, and one or more sub pictures may beextracted from a picture. In certain environments, one or more codedsub-pictures may be assembled in the compressed domain withouttranscoding to the sample level into a coded picture, and in the same orother cases, one or more coded sub-pictures may be extracted from acoded picture in the compressed domain.

Adaptive Resolution Change (ARC) may refer to mechanisms that allow thechange of resolution of a picture or sub-picture within a coded videosequence, by the means of, for example, reference picture resampling.ARC parameters henceforth refer to the control information required toperform adaptive resolution change, that may include, for example,filter parameters, scaling factors, resolutions of output and/orreference pictures, various control flags, and so forth.

In embodiments coding and decoding may be performed on a single,semantically independent coded video picture. Before describing theimplication of coding/decoding of multiple sub pictures with independentARC parameters and its implied additional complexity, options forsignaling ARC parameters shall be described.

Referring to FIGS. 5A-5E, shown are several embodiments for signalingARC parameters. As noted with each of the embodiments, they may havecertain advantages and certain disadvantages from a coding efficiency,complexity, and architecture viewpoint. A video coding standard ortechnology may choose one or more of these embodiments, or options knownfrom related art, for signaling ARC parameters. The embodiments may notbe mutually exclusive, and conceivably may be interchanged based onapplication needs, standards technology involved, or encoder's choice.

Classes of ARC parameters may include:

-   -   Upsample and/or downsample factors, separate or combined in X        and Y dimension.    -   Upsample and/or downsample factors, with an addition of a        temporal dimension, indicating constant speed zoom in/out for a        given number of pictures.    -   Either of the above two may involve the coding of one or more        presumably short syntax elements that may point into a table        containing the factor(s).    -   Resolution, in X or Y dimension, in units of samples, blocks,        macroblocks, coding units (CUs), or any other suitable        granularity, of the input picture, output picture, reference        picture, coded picture, combined or separately. If there is more        than one resolution (such as, for example, one for input        picture, one for reference picture) then, in certain cases, one        set of values may be inferred to from another set of values.        Such could be gated, for example, by the use of flags. For a        more detailed example, see below.    -   “Warping” coordinates akin those used in H.263 Annex P, again in        a suitable granularity as described above. H.263 Annex P defines        one efficient way to code such warping coordinates, but other,        potentially more efficient ways could conceivably also be        devised. For example, the variable length reversible,        “Huffman”-style coding of warping coordinates of Annex P could        be replaced by a suitable length binary coding, where the length        of the binary code word could, for example, be derived from a        maximum picture size, possibly multiplied by a certain factor        and offset by a certain value, so to allow for “warping” outside        of the maximum picture size's boundaries.    -   upsample and/or downsample filter parameters. In embodiments,        there may be only a single filter for upsampling and/or        downsampling. However, in embodiments, it can be desirable to        allow more flexibility in filter design, and that may require to        signaling of filter parameters. Such parameters may be selected        through an index in a list of possible filter designs, the        filter may be fully specified (for example through a list of        filter coefficients, using suitable entropy coding techniques),        the filter may be implicitly selected through upsample and/or        downsample ratios according which in turn are signaled according        to any of the mechanisms mentioned above, and so forth.

Henceforth, the description assumes the coding of a finite set ofupsample and/or downsample factors (the same factor to be used in both Xand Y dimension), indicated through a codeword. That codeword may bevariable length coded, for example using the Ext-Golomb code common forcertain syntax elements in video coding specifications such as H.264 andH.265. One suitable mapping of values to upsample and/or downsamplefactors can, for example, be according to Table 1:

TABLE 1 Codeword Ext-Golomb Code Original/Target resolution 0 1   1/1 1010   1/1.5 (upscale by 50%) 2 011 1.5/1 (downscale by 50%) 3 00100  1/2 (upscale by 100%) 4 00101   2/1 (downscale by 100%)

Many similar mappings could be devised according to the needs of anapplication and the capabilities of the up and downscale mechanismsavailable in a video compression technology or standard. The table couldbe extended to more values. Values may also be represented by entropycoding mechanisms other than Ext-Golomb codes, for example using binarycoding. That may have certain advantages when the resampling factorswere of interest outside the video processing engines (encoder anddecoder foremost) themselves, for example by MANEs. It should be notedthat, for situations where no resolution change is required, anExt-Golomb code can be chosen that is short; in the table above, only asingle bit. That can have a coding efficiency advantage over usingbinary codes for the most common case.

The number of entries in the table, as well as their semantics, may befully or partially configurable. For example, the basic outline of thetable may be conveyed in a “high” parameter set such as a sequence ordecoder parameter set. In embodiments, one or more such tables may bedefined in a video coding technology or standard, and may be selectedthrough for example a decoder or sequence parameter set.

Below is described how an upsample and/or downsample factor (ARCinformation), coded as described above, may be included in a videocoding technology or standard syntax. Similar considerations may applyto one, or a few, codewords controlling upsample and/or downsamplefilters. See below for a discussion when comparatively large amounts ofdata are required for a filter or other data structures.

As shown in FIG. 5A, H.263 Annex P includes the ARC information (502) inthe form of four warping coordinates into the picture header (501),specifically in the H.263 PLUSPTYPE (503) header extension. This can bea sensible design choice when a) there is a picture header available,and b) frequent changes of the ARC information are expected. However,the overhead when using H.263-style signaling can be quite high, andscaling factors may not pertain among picture boundaries as pictureheader can be of transient nature.

As shown in FIG. 5B, JVCET-M135-vl includes the ARC referenceinformation (505) (an index) located in a picture parameter set (504),indexing a table (506) including target resolutions that in turn islocated inside a sequence parameter set (507). The placement of thepossible resolution in a table (506) in the sequence parameter set (507)can, according to verbal statements made by the authors, be justified byusing the SPS as an interoperability negotiation point during capabilityexchange. Resolution can change, within the limits set by the values inthe table (506) from picture to picture by referencing the appropriatepicture parameter set (504).

Referring to FIGS. 5C-5E, the following embodiments may exist to conveyARC information in a video bitstream. Each of those options has certainadvantages over embodiments described above. Embodiments may besimultaneously present in the same video coding technology or standard.

In embodiments, for example the embodiment shown in FIG. 5C, ARCinformation (509) such as a resampling (zoom) factor may be present in aslice header, GOP header, tile header, or tile group header. FIG. 5Cillustrates an embodiment in which tile group header (508) is used. Thiscan be adequate if the ARC information is small, such as a singlevariable length ue(v) or fixed length codeword of a few bits, forexample as shown above. Having the ARC information in a tile groupheader directly has the additional advantage of the ARC information maybe applicable to a sub picture represented by, for example, that tilegroup, rather than the whole picture. See also below. In addition, evenif the video compression technology or standard envisions only wholepicture adaptive resolution changes (in contrast to, for example, tilegroup based adaptive resolution changes), putting the ARC informationinto the tile group header vis a vis putting it into an H.263-stylepicture header has certain advantages from an error resilienceviewpoint.

In embodiments, for example the embodiment shown in FIG. 5D, the ARCinformation (512) itself may be present in an appropriate parameter setsuch as, for example, a picture parameter set, header parameter set,tile parameter set, adaptation parameter set, and so forth. FIG. 5Dillustrates an embodiment in which adaptation parameter set (511) isused. The scope of that parameter set can advantageously be no largerthan a picture, for example a tile group. The use of the ARC informationis implicit through the activation of the relevant parameter set. Forexample, when a video coding technology or standard contemplates onlypicture-based ARC, then a picture parameter set or equivalent may beappropriate.

In embodiments, for example the embodiment shown in FIG. 5E, ARCreference information (513) may be present in a Tile Group header (514)or a similar data structure. That reference information (513) can referto a subset of ARC information (515) available in a parameter set (516)with a scope beyond a single picture, for example a sequence parameterset, or decoder parameter set.

As shown in FIG. 6A, a tile group header (601) as an exemplary syntaxstructure of a header applicable to a (possibly rectangular) part of apicture can conditionally contain, a variable length, Exp-Golomb codedsyntax element dec_pic_size_idx (602) (depicted in boldface). Thepresence of this syntax element in the tile group header can be gated onthe use of adaptive resolution (603)—here, the value of a flag notdepicted in boldface, which means that flag is present in the bitstreamat the point where it occurs in the syntax diagram. Whether or notadaptive resolution is in use for this picture or parts thereof can besignaled in any high level syntax structure inside or outside thebitstream. In the example shown, it is signaled in the sequenceparameter set as outlined below.

Referring to FIG. 6B, shown is also an excerpt of a sequence parameterset (610). The first syntax element shown isadaptive_pic_resolution_change_flag (611). When true, that flag canindicate the use of adaptive resolution which, in turn may requirecertain control information. In the example, such control information isconditionally present based on the value of the flag based on the if( )statement in the parameter set (612) and the tile group header (601).

When adaptive resolution is in use, in this example, coded is an outputresolution in units of samples (613). The numeral 613 refers to bothoutput_pic_width_in_luma_samples and output_pic_height_in_luma_samples,which together can define the resolution of the output picture.Elsewhere in a video coding technology or standard, certain restrictionsto either value can be defined. For example, a level definition maylimit the number of total output samples, which could be the product ofthe value of those two syntax elements. Also, certain video codingtechnologies or standards, or external technologies or standards suchas, for example, system standards, may limit the numbering range (forexample, one or both dimensions must be divisible by a power of 2number), or the aspect ratio (for example, the width and height must bein a relation such as 4:3 or 16:9). Such restrictions may be introducedto facilitate hardware implementations or for other reasons, and arewell known in the art.

In certain applications, it can be advisable that the encoder instructsthe decoder to use a certain reference picture size rather thanimplicitly assume that size to be the output picture size. In thisexample, the syntax element reference_pic_size_present_flag (614) gatesthe conditional presence of reference picture dimensions (615) (again,the numeral refers to both width and height).

Finally, shown is a table of possible decoding picture width andheights. Such a table can be expressed, for example, by a tableindication (num_dec_pic_size_in_luma_samples_minus1) (616). The “minus1”can refer to the interpretation of the value of that syntax element. Forexample, if the coded value is zero, one table entry is present. If thevalue is five, six table entries are present. For each “line” in thetable, decoded picture width and height are then included in the syntax(617).

The table entries presented (617) can be indexed using the syntaxelement dec_pic_size_idx (602) in the tile group header, therebyallowing different decoded sizes—in effect, zoom factors-per tile group.

Certain video coding technologies or standards, for example VP9, supportspatial scalability by implementing certain forms of reference pictureresampling (signaled quite differently from the disclosed subjectmatter) in conjunction with temporal scalability, so to enable spatialscalability. In particular, certain reference pictures may be upsampledusing ARC-style technologies to a higher resolution to form the base ofa spatial enhancement layer. Those upsampled pictures could be refined,using normal prediction mechanisms at the high resolution, so to adddetail.

Embodiments discussed herein can be used in such an environment. Incertain cases, in the same or another embodiment, a value in the NALunit header, for example the Temporal ID field, can be used to indicatenot only the temporal but also the spatial layer. Doing so may havecertain advantages for certain system designs; for example, existingSelected Forwarding Units (SFU) created and optimized for temporal layerselected forwarding based on the NAL unit header Temporal ID value canbe used without modification, for scalable environments. In order toenable that, there may be a requirement for a mapping between the codedpicture size and the temporal layer is indicated by the temporal IDfield in the NAL unit header.

In some video coding technologies, an Access Unit (AU) can refer tocoded picture(s), slice(s), tile(s), NAL Unit(s), and so forth, thatwere captured and composed into a the respective picture, slice, tile,and/or NAL unit bitstream at a given instance in time. That instance intime can be, for example, the composition time.

In HEVC, and certain other video coding technologies, a picture ordercount (POC) value can be used for indicating a selected referencepicture among multiple reference pictures stored in a decoded picturebuffer (DPB). When an access unit (AU) includes one or more pictures,slices, or tiles, each picture, slice, or tile belonging to the same AUmay carry the same POC value, from which it can be derived that theywere created from content of the same composition time. In other words,in a scenario where two pictures/slices/tiles carry the same given POCvalue, that can be indicative of the two picture/slice/tile belonging tothe same AU and having the same composition time. Conversely, twopictures/tiles/slices having different POC values can indicate thatthose pictures/slices/tiles belong to different AUs and have differentcomposition times.

In embodiments, this rigid relationship can be relaxed in that an accessunit can include pictures, slices, or tiles with different POC values.By allowing different POC values within an AU, it becomes possible touse the POC value to identify potentially independently decodablepictures/slices/tiles with identical presentation time. That, in turn,can enable support of multiple scalable layers without a change ofreference picture selection signaling, for example reference picture setsignaling or reference picture list signaling, as described in moredetail below.

It is, however, still desirable to be able to identify the AU apicture/slice/tile belongs to, with respect to otherpicture/slices/tiles having different POC values, from the POC valuealone. This can be achieved, as described below.

In embodiments, an access unit count (AUC) may be signaled in ahigh-level syntax structure, such as NAL unit header, slice header, tilegroup header, SEI message, parameter set or AU delimiter. The value ofAUC may be used to identify which NAL units, pictures, slices, or tilesbelong to a given AU. The value of AUC may be corresponding to adistinct composition time instance. The AUC value may be equal to amultiple of the POC value. By diving the POC value by an integer value,the AUC value may be calculated. In certain cases, division operationscan place a certain burden on decoder implementations. In such cases,small restrictions in the numbering space of the AUC values may allowsubstituting the division operation with shift operations. For example,the AUC value may be equal to a Most Significant Bit (MSB) value of thePOC value range.

In embodiments, a value of POC cycle per AU (poc_cycle_au) may besignaled in a high-level syntax structure, such as NAL unit header,slice header, tile group header, SEI message, parameter set or AUdelimiter. The poc_cycle_au may indicate how many different andconsecutive POC values can be associated with the same AU. For example,if the value of poc_cycle_au is equal to 4, the pictures, slices ortiles with the POC value equal to 0-3, inclusive, may be associated withthe AU with AUC value equal to 0, and the pictures, slices or tiles withPOC value equal to 4-7, inclusive, may be associated with the AU withAUC value equal to 1. Hence, the value of AUC may be inferred bydividing the POC value by the value of poc_cycle_au.

In embodiments, the value of poc_cycle_au may be derived frominformation, located for example in the video parameter set (VPS), thatidentifies the number of spatial or SNR layers in a coded videosequence. An example of such a possible relationship is brieflydescribed below. While the derivation as described above may save a fewbits in the VPS and hence may improve coding efficiency, in someembodiments the poc_cycle_au may be explicitly coded in an appropriatehigh level syntax structure hierarchically below the video parameterset, so to be able to minimize poc_cycle_au for a given small part of abitstream such as a picture. This optimization may save more bits thancan be saved through the derivation process above because POC values,and/or values of syntax elements indirectly referring to POC, may becoded in low level syntax structures.

In embodiments, FIG. 8 shows an example of syntax tables to signal thesyntax element of vps_poc_cycle_au in VPS (or SPS), which indicates thepoc_cycle_au used for all picture/slices in a coded video sequence, andthe syntax element of slice_poc_cycle_au, which indicates thepoc_cycle_au of the current slice, in slice header. If the POC valueincreases uniformly per AU, vps_contant_poc_cycle_per_au in VPS may beset equal to 1 and vps_poc_cycle_au may be signaled in VPS. In thiscase, slice_poc_cycle_au may be not explicitly signaled, and the valueof AUC for each AU may be calculated by dividing the value of POC byvps_poc_cycle_au. If the POC value does not increase uniformly per AU,vps_contant_poc_cycle_per_au in VPS may be set equal to 0. In this case,vps_access_unit_cnt may be not signaled, while slice_access_unit_cnt maybe signaled in slice header for each slice or picture. Each slice orpicture may have a different value of slice_access_unit_cnt. The valueof AUC for each AU may be calculated by dividing the value of POC byslice_poc_cycle_au.

FIG. 9 shows a block diagram illustrating an example of the processabove. For example, in operation 5910, the VPS (or SPS) can be parsed,and it can be determined whether the POC cycle per AU is constant withinthe coded video sequence at operation 5920. If the POC cycle per AU isconstant (YES at operation 5920), then the value of access unit countfor a particular access unit can be calculated from the poc_cycle_ausignaled for the coded video sequence and a POC value of the particularaccess unit at operation 5930. If the POC cycle per AU is not constant(NO at operation 5920), then then the value of access unit count for aparticular access unit can be calculated from the poc_cycle_au signaledat the picture level and the POC value of the particular access unit atoperation 5940. At operation 5950, a new VPS (or SPS) can be parsed.

In embodiments, even though the value of POC of a picture, slice, ortile may be different, the picture, slice, or tile corresponding to anAU with the same AUC value may be associated with the same decoding oroutput time instance. Hence, without any inter-parsing/decodingdependency across pictures, slices or tiles in the same AU, all orsubset of pictures, slices or tiles associated with the same AU may bedecoded in parallel, and may be outputted at the same time instance.

In embodiments, even though the value of POC for a picture, slice, ortile may be different, the picture, slice, or tile corresponding to anAU with the same AUC value may be associated with the samecomposition/display time instance. When the composition time iscontained in a container format, even though pictures correspond todifferent AUs, if the pictures have the same composition time, thepictures can be displayed at the same time instance.

In embodiments, each picture, slice, or tile may have the same temporalidentifier (temporal_id) in the same AU. All or a subset of pictures,slices or tiles corresponding to a time instance may be associated withthe same temporal sub-layer. In embodiments, each picture, slice, ortile may have the same or a different spatial layer id (layer_id) in thesame AU. All or subset of pictures, slices or tiles corresponding to atime instance may be associated with the same or a different spatiallayer.

FIG. 7 shows an example of a video sequence structure with combinationof temporal_id, layer_id, POC and AUC values with adaptive resolutionchange. In this example, a picture, slice or tile in the first AU withAUC=0 may have temporal_id=0 and layer_id=0 or 1, while a picture, sliceor tile in the second AU with AUC=1 may have temporal_id=1 andlayer_id=0 or 1, respectively. The value of POC is increased by 1 perpicture regardless of the values of temporal_id and layer_id. In thisexample, the value of poc_cycle_au can be equal to 2. In embodiments,the value of poc_cycle_au may be set equal to the number of (spatialscalability) layers. In this example, hence, the value of POC isincreased by 2, while the value of AUC is increased by 1.

In the above embodiments, all or sub-set of inter-picture or inter-layerprediction structure and reference picture indication may be supportedby using the existing reference picture set (RPS) signaling in HEVC orthe reference picture list (RPL) signaling. In RPS or RPL, the selectedreference picture may be indicated by signaling the value of POC or thedelta value of POC between the current picture and the selectedreference picture. In embodiments, the RPS and RPL can be used toindicate the inter-picture or inter-layer prediction structure withoutchange of signaling, but with the following restrictions. If the valueof temporal_id of a reference picture is greater than the value oftemporal_id current picture, the current picture may not use thereference picture for motion compensation or other predictions. If thevalue of layer_id of a reference picture is greater than the value oflayer_id current picture, the current picture may not use the referencepicture for motion compensation or other predictions.

In embodiments, the motion vector scaling based on POC difference fortemporal motion vector prediction may be disabled across multiplepictures within an access unit. Hence, although each picture may have adifferent POC value within an access unit, the motion vector is notscaled and used for temporal motion vector prediction within an accessunit. This is because a reference picture with a different POC in thesame AU is considered a reference picture having the same time instance.Therefore, in the embodiment, the motion vector scaling function mayreturn 1, when the reference picture belongs to the AU associated withthe current picture.

In embodiments, the motion vector scaling based on POC difference fortemporal motion vector prediction may be optionally disabled acrossmultiple pictures, when the spatial resolution of the reference pictureis different from the spatial resolution of the current picture. Whenthe motion vector scaling is allowed, the motion vector is scaled basedon both POC difference and the spatial resolution ratio between thecurrent picture and the reference picture.

In embodiments, the motion vector may be scaled based on AUC differenceinstead of POC difference, for temporal motion vector prediction,especially when the poc_cycle_au has non-uniform value (for example whenvps_contant_poc_cycle_per_au==0). Otherwise (for example whenvps_contant_poc_cycle_per_au==1), the motion vector scaling based on AUCdifference may be identical to the motion vector scaling based on POCdifference.

In embodiments, when the motion vector is scaled based on AUCdifference, the reference motion vector in the same AU (with the sameAUC value) with the current picture is not scaled based on AUCdifference and used for motion vector prediction without scaling or withscaling based on spatial resolution ratio between the current pictureand the reference picture.

In embodiments, the AUC value may be used for identifying the boundaryof AU and used for hypothetical reference decoder (HRD) operation, whichneeds input and output timing with AU granularity. In embodiments, thedecoded picture with the highest layer in an AU may be outputted fordisplay. The AUC value and the layer_id value can be used foridentifying the output picture.

In embodiments, a picture may include of one or more sub-pictures. Eachsub-picture may cover a local region or the entire region of thepicture. The region supported by a sub-picture may or may not beoverlapped with the region supported by another sub-picture. The regioncovered by one or more sub-pictures may or may not cover the entireregion of a picture. If a picture includes a sub-picture, the regionsupported by the sub-picture may be identical to the region supported bythe picture.

In embodiments, a sub-picture may be coded by a coding method similar tothe coding method used for the coded picture. A sub-picture may beindependently coded or may be coded dependent on another sub-picture ora coded picture. A sub-picture may or may not have any parsingdependency from another sub-picture or a coded picture.

In embodiments, a coded sub-picture may be contained in one or morelayers. A coded sub-picture in a layer may have a different spatialresolution. The original sub-picture may be spatially re-sampled (forexample up-sampled or down-sampled), coded with different spatialresolution parameters, and contained in a bitstream corresponding to alayer.

In embodiments, a sub-picture with (W, H), where W indicates the widthof the sub-picture and H indicates the height of the sub-picture,respectively, may be coded and contained in the coded bitstreamcorresponding to layer 0, while the up-sampled (or down-sampled)sub-picture from the sub-picture with the original spatial resolution,with (W*S_(w,k), H*S_(h,k)), may be coded and contained in the codedbitstream corresponding to layer k, where S_(w,k), S_(h,k) indicate theresampling ratios, horizontally and vertically. If the values ofS_(w,k), S_(h,k) are greater than 1, the resampling may be up-sampling.Whereas, if the values of S_(w,k), S_(h,k) are smaller than 1, theresampling may be down-sampling.

In embodiments, a coded sub-picture in a layer may have a differentvisual quality from that of the coded sub-picture in another layer inthe same sub-picture or different subpicture. For example, sub-picture iin a layer, n, may be coded with the quantization parameter, Q_(i,n),while a sub-picture j in a layer, m, may be coded with the quantizationparameter, Q_(j,m).

In embodiments, a coded sub-picture in a layer may be independentlydecodable, without any parsing or decoding dependency from a codedsub-picture in another layer of the same local region. The sub-picturelayer, which can be independently decodable without referencing anothersub-picture layer of the same local region, may be the independentsub-picture layer. A coded sub-picture in the independent sub-picturelayer may or may not have a decoding or parsing dependency from apreviously coded sub-picture in the same sub-picture layer, but thecoded sub-picture may not have any dependency from a coded picture inanother sub-picture layer.

In embodiments, a coded sub-picture in a layer may be dependentlydecodable, with any parsing or decoding dependency from a codedsub-picture in another layer of the same local region. The sub-picturelayer, which can be dependently decodable with referencing anothersub-picture layer of the same local region, may be the dependentsub-picture layer. A coded sub-picture in the dependent sub-picture mayreference a coded sub-picture belonging to the same sub-picture, apreviously coded sub-picture in the same sub-picture layer, or bothreference sub-pictures.

In embodiments, a coded sub-picture may include one or more independentsub-picture layers and one or more dependent sub-picture layers.However, at least one independent sub-picture layer may be present for acoded sub-picture. A value of the layer identifier (layer_id), which maybe present in NAL unit header or another high-level syntax structure, ofthe independent sub-picture layer may be equal to 0. The sub-picturelayer with the layer_id equal to 0 may be the base sub-picture layer.

In embodiments, a picture may include one or more foregroundsub-pictures and one background sub-picture. The region supported by abackground sub-picture may be equal to the region of the picture. Theregion supported by a foreground sub-picture may be overlapped with theregion supported by a background sub-picture. The background sub-picturemay be a base sub-picture layer, while the foreground sub-picture may bea non-base (enhancement) sub-picture layer. One or more non-basesub-picture layers may reference the same base layer for decoding. Eachnon-base sub-picture layer with layer_id equal to a may reference anon-base sub-picture layer with layer_id equal to b, where a is greaterthan b.

In embodiments, a picture may include one or more foregroundsub-pictures with or without a background sub-picture. Each sub-picturemay have its own base sub-picture layer and one or more non-base(enhancement) layers. Each base sub-picture layer may be referenced byone or more non-base sub-picture layers. Each non-base sub-picture layerwith layer_id equal to a may reference a non-base sub-picture layer withlayer_id equal to b, where a is greater than b.

In embodiments, a picture may include one or more foregroundsub-pictures with or without a background sub-picture. Each codedsub-picture in a (base or non-base) sub-picture layer may be referencedby one or more non-base layer sub-pictures belonging to the samesub-picture and one or more non-base layer sub-pictures, which are notbelonging to the same sub-picture.

In embodiments, a picture may include one or more foregroundsub-pictures with or without a background sub-picture. A sub-picture ina layer a may be further partitioned into multiple sub-pictures in thesame layer. One or more coded sub-pictures in a layer b may referencethe partitioned sub-picture in a layer a.

In embodiments, a coded video sequence (CVS) may be a group of the codedpictures. The CVS may include one or more coded sub-picture sequences(CSPS), where the CSPS may be a group of coded sub-pictures covering thesame local region of the picture. A CSPS may have the same or adifferent temporal resolution than that of the coded video sequence.

In embodiments, a CSPS may be coded and contained in one or more layers.A CSPS may include one or more CSPS layers. Decoding one or more CSPSlayers corresponding to a CSPS may reconstruct a sequence ofsub-pictures corresponding to the same local region.

In embodiments, the number of CSPS layers corresponding to a CSPS may beidentical to or different from the number of CSPS layers correspondingto another CSPS.

In embodiments, a CSPS layer may have a different temporal resolution(e.g. frame rate) from another CSPS layer. The original (uncompressed)sub-picture sequence may be temporally re-sampled (for exampleup-sampled or down-sampled), coded with different temporal resolutionparameters, and contained in a bitstream corresponding to a layer.

In embodiments, a sub-picture sequence with the frame rate, F, may becoded and contained in the coded bitstream corresponding to layer 0,while the temporally up-sampled (or down-sampled) sub-picture sequencefrom the original sub-picture sequence, with F*S_(t,k), may be coded andcontained in the coded bitstream corresponding to layer k, where S_(t,k)indicates the temporal sampling ratio for layer k. If the value ofS_(t,k) is greater than 1, the temporal resampling process may be framerate up conversion. Whereas, if the value of S_(t,k) is smaller than 1,the temporal resampling process may be frame rate down conversion.

In embodiments, when a sub-picture with a CSPS layer a is referenced bya sub-picture with a CSPS layer b for motion compensation or anyinter-layer prediction, if the spatial resolution of the CSPS layer a isdifferent from the spatial resolution of the CSPS layer b, decodedpixels in the CSPS layer a are resampled and used for reference. Theresampling process may use an up-sampling filtering or a down-samplingfiltering.

FIG. 10 shows an example video stream including a background video CSPSwith layer_id equal to 0 and multiple foreground CSPS layers. While acoded sub-picture may include one or more CSPS layers, a backgroundregion, which does not belong to any foreground CSPS layer, may includea base layer. The base layer may contain a background region andforeground regions, while an enhancement CSPS layer may contain aforeground region. An enhancement CSPS layer may have a better visualquality than the base layer, at the same region. The enhancement CSPSlayer may reference the reconstructed pixels and the motion vectors ofthe base layer, corresponding to the same region.

In embodiments, the video bitstream corresponding to a base layer iscontained in a track, while the CSPS layers corresponding to eachsub-picture are contained in a separated track, in a video file.

In embodiments, the video bitstream corresponding to a base layer iscontained in a track, while CSPS layers with the same layer_id arecontained in a separated track. In this example, a track correspondingto a layer k includes CSPS layers corresponding to the layer k, only.

In embodiments, each CSPS layer of each sub-picture is stored in aseparate track. Each track may or may not have any parsing or decodingdependency from one or more other tracks.

In embodiments, each track may contain bitstreams corresponding to layeri to layer j of CSPS layers of all or a subset of sub-pictures, where0<i=<j=<k, k being the highest layer of CSPS.

In embodiments, a picture includes one or more associated media dataincluding depth map, alpha map, 3D geometry data, occupancy map, etc.Such associated timed media data can be divided to one or multiple datasub-stream each of which corresponding to one sub-picture.

FIG. 11 shows an example of video conference based on the multi-layeredsub-picture method. In a video stream, one base layer video bitstreamcorresponding to the background picture and one or more enhancementlayer video bitstreams corresponding to foreground sub-pictures arecontained. Each enhancement layer video bitstream may correspond to aCSPS layer. In a display, the picture corresponding to the base layer isdisplayed by default. It contains one or more user's picture in apicture (PIP). When a specific user is selected by a client's control,the enhancement CSPS layer corresponding to the selected user may bedecoded and displayed with the enhanced quality or spatial resolution.

FIG. 12 shows a block diagram illustrating an example of the processabove. For example, in operation S1210, a video bitstream with multiplelayers can be decoded. In operation S1220, a background region and oneor more foreground sub-pictures can be identified. At operation S1230,it can be determined whether a specific sub-picture region, for exampleone of the foreground sub-pictures, is selected. If a specificsub-picture region is selected (YES at operation S1240), an enhancedsub-picture may be decoded and displayed. If a specific sub-pictureregion is not selected (NO at operation S1240), the background regionmay be decoded and displayed

In embodiments, a network middle box (for example a router) may select asubset of layers to send to a user depending on its bandwidth. Thepicture/subpicture organization may be used for bandwidth adaptation.For instance, if the user doesn't have the bandwidth, the router stripsof layers or selects some subpictures due to their importance or basedon used setup and this can be done dynamically to adopt to bandwidth.

FIG. 13 shows an embodiment relating to a use case of 360 video. When aspherical 360 picture, for example picture 1310, is projected onto aplanar picture, the projection 360 picture may be partitioned intomultiple sub-pictures as a base layer. For example, the multiplesub-pictures may include a back sub-picture, a top sub-picture, a rightsub-picture, a left sub-picture, a forward sub-picture, and a bottomsub-picture. An enhancement layer of a specific sub-picture, for examplea forward sub-picture, may be coded and transmitted to a client. Adecoder may be able to decode both the base layer including allsub-pictures and an enhancement layer of a selected sub-picture. Whenthe current viewport is identical to the selected sub-picture, thedisplayed picture may have a higher quality with the decoded sub-picturewith the enhancement layer. Otherwise, the decoded picture with the baselayer can be displayed, with a lower quality.

In embodiments, any layout information for display may be present in afile, as supplementary information (such as SEI message or metadata).One or more decoded sub-pictures may be relocated and displayeddepending on the signaled layout information. The layout information maybe signaled by a streaming server or a broadcaster, or may beregenerated by a network entity or a cloud server, or may be determinedby a user's customized setting.

In embodiments, when an input picture is divided into one or more(rectangular) sub-region(s), each sub-region may be coded as anindependent layer. Each independent layer corresponding to a localregion may have a unique layer_id value. For each independent layer, thesub-picture size and location information may be signaled. For example,picture size (width, height), the offset information of the left-topcorner (x_offset, y_offset). FIG. 14 shows an example of the layout ofdivided sub-pictures, its sub-picture size and position information andits corresponding picture prediction structure. The layout informationincluding the sub-picture size(s) and the sub-picture position(s) may besignaled in a high-level syntax structure, such as parameter set(s),header of slice or tile group, or SEI message.

In embodiments, each sub-picture corresponding to an independent layermay have its unique POC value within an AU. When a reference pictureamong pictures stored in DPB is indicated by using syntax element(s) inRPS or RPL structure, the POC value(s) of each sub-picture correspondingto a layer may be used.

In embodiments, in order to indicate the (inter-layer) predictionstructure, the layer_id may not be used and the POC (delta) value may beused.

In embodiments, a sub-picture with a POC vale equal to N correspondingto a layer (or a local region) may or may not be used as a referencepicture of a sub-picture with a POC value equal to N+K, corresponding tothe same layer (or the same local region) for motion compensatedprediction. In most cases, the value of the number K may be equal to themaximum number of (independent) layers, which may be identical to thenumber of sub-regions.

In embodiments, FIG. 15 shows an extended case of FIG. 14 . When aninput picture is divided into multiple (e.g. four) sub-regions, eachlocal region may be coded with one or more layers. In the case, thenumber of independent layers may be equal to the number of sub-regions,and one or more layers may correspond to a sub-region. Thus, eachsub-region may be coded with one or more independent layer(s) and zeroor more dependent layer(s).

In embodiments, in FIG. 15 , the input picture may be divided into foursub-regions. As an example, the right-top sub-region may be coded as twolayers, which are layer 1 and layer 4, while the right-bottom sub-regionmay be coded as two layers, which are layer 3 and layer 5. In this case,the layer 4 may reference the layer 1 for motion compensated prediction,while the layer 5 may reference the layer 3 for motion compensation.

In embodiments, in-loop filtering (such as deblocking filtering,adaptive in-loop filtering, reshaper, bilateral filtering or anydeep-learning based filtering) across layer boundary may be (optionally)disabled.

In embodiments, motion compensated prediction or intra-block copy acrosslayer boundary may be (optionally) disabled.

In embodiments, boundary padding for motion compensated prediction orin-loop filtering at the boundary of sub-picture may be processedoptionally. A flag indicating whether the boundary padding is processedor not may be signaled in a high-level syntax structure, such asparameter set(s) (VPS, SPS, PPS, or APS), slice or tile group header, orSEI message.

In embodiments, the layout information of sub-region(s) (orsub-picture(s)) may be signaled in VPS or SPS. FIG. 16A shows an exampleof the syntax elements in VPS, and FIG. 16B shows an example of thesyntax elements in SPS. In this example, vps_sub_picture_dividing_flagis signaled in VPS. The flag may indicate whether input picture(s) aredivided into multiple sub-regions or not. When the value ofvps_sub_picture_dividing_flag is equal to 0, the input picture(s) in thecoded video sequence(s) corresponding to the current VPS may not bedivided into multiple sub-regions. In this case, the input picture sizemay be equal to the coded picture size (pic_width_in_luma_samples,pic_height_in_luma_samples), which is signaled in SPS. When the value ofvps_sub_picture_dividing_flag is equal to 1, the input picture(s) may bedivided into multiple sub-regions. In this case, the syntax elementsvps_full_pic_width_in_luma_samples andvps_full_pic_height_in_luma_samples are signaled in VPS. The values ofvps_full_pic_width_in_luma_samples andvps_full_pic_height_in_luma_samples may be equal to the width and heightof the input picture(s), respectively.

In embodiments, the values of vps_full_pic_width_in_luma_samples andvps_full_pic_height_in_luma_samples may not be used for decoding, butmay be used for composition and display.

In embodiments, when the value of vps_sub_picture_dividing_flag is equalto 1, the syntax elements pic_offset_x and pic_offset_y may be signaledin SPS, which corresponds to (a) specific layer(s). In this case, thecoded picture size (pic_width_in_luma_samples,pic_height_in_luma_samples) signaled in SPS may be equal to the widthand height of the sub-region corresponding to a specific layer. Also,the position (pic_offset_x, pic_offset_y) of the left-top corner of thesub-region may be signaled in SPS.

In embodiments, the position information (pic_offset_x, pic_offset_y) ofthe left-top corner of the sub-region may not be used for decoding, butmay be used for composition and display.

In embodiments, the layout information (size and position) of all orsub-set sub-region(s) of (an) input picture(s), the dependencyinformation between layer(s) may be signaled in a parameter set or anSEI message. FIG. 17 shows an example of syntax elements to indicate theinformation of the layout of sub-regions, the dependency between layers,and the relation between a sub-region and one or more layers. In thisexample, the syntax element num_sub_region indicates the number of(rectangular) sub-regions in the current coded video sequence. thesyntax element num_layers indicates the number of layers in the currentcoded video sequence. The value of num_layers may be equal to or greaterthan the value of num_sub_region. When any sub-region is coded as asingle layer, the value of num_layers may be equal to the value ofnum_sub_region. When one or more sub-regions are coded as multiplelayers, the value of num_layers may be greater than the value ofnum_sub_region. The syntax element direct_dependency_flag[i][j]indicates the dependency from the j-th layer to the i-th layer.num_layers_for_region[i] indicates the number of layers associated withthe i-th sub-region. sub_region_layer_id[i][j] indicates the layer_id ofthe j-th layer associated with the i-th sub-region. Thesub_region_offset_x[i] and sub_region_offset_y[i] indicate thehorizontal and vertical location of the left-top corner of the i-thsub-region, respectively. The sub_region_width [i] andsub_region_height[i] indicate the width and height of the i-thsub-region, respectively.

In embodiments, one or more syntax elements that specify the outputlayer set to indicate one of more layers to be outputted with or withoutprofile tier level information may be signaled in a high-level syntaxstructure, e.g. VPS, DPS, SPS, PPS, APS or SEI message. Referring toFIG. 18 , the syntax element num_output_layer_sets indicating the numberof output layer set (OLS) in the coded vide sequence referring to theVPS may be signaled in the VPS. For each output layer set,output_layer_flag may be signaled as many as the number of outputlayers.

In embodiments, output_layer_flag[i] equal to 1 specifies that the i-thlayer is output. vps_output_layer_flag[i] equal to 0 specifies that thei-th layer is not output.

In embodiments, one or more syntax elements that specify the profiletier level information for each output layer set may be signaled in ahigh-level syntax structure, e.g. VPS, DPS, SPS, PPS, APS or SEImessage. Still referring to FIG. 18 , the syntax elementnum_profile_tile_level indicating the number of profile tier levelinformation per OLS in the coded vide sequence referring to the VPS maybe signaled in the VPS. For each output layer set, a set of syntaxelements for profile tier level information or an index indicating aspecific profile tier level information among entries in the profiletier level information may be signaled as many as the number of outputlayers.

In embodiments, profile_tier_level_idx[i][j] specifies the index, intothe list of profile_tier_level( ) syntax structures in the VPS, of theprofile_tier_level( ) syntax structure that applies to the j-th layer ofthe i-th OLS.

In embodiments, referring to FIG. 19 , the syntax elementsnum_profile_tile_level and/or num_output_layer_sets may be signaled whenthe number of maximum layers is greater than 1(vps_max_layers_minus1>0).

In embodiments, referring to FIG. 19 , the syntax elementvps_output_layers_mode[i] indicating the mode of output layer signalingfor the i-th output layer set may be present in VPS.

In embodiments, vps_output_layers_mode[i] equal to 0 specifies that onlythe highest layer is output with the i-th output layer set.vps_output_layer_mode[i] equal to 1 specifies that all layers are outputwith the i-th output layer set. vps_output_layer_mode[i] equal to 2specifies that the layers that are output are the layers withvps_output_layer_flag[i][j] equal to 1 with the i-th output layer set.More values may be reserved.

In embodiments, the output_layer_flag[i][j] may or may not be signaleddepending on the value of vps_output_layers_mode[i] for the i-th outputlayer set.

In embodiments, referring to FIG. 19 , the flag vps_ptl_signal_flag[i]may be present for the i-th output layer set. Depending the value ofvps_ptl_signal_flag[i], the profile tier level information for the i-thoutput layer set may or may not be signaled.

In embodiments, referring to FIG. 20 , the number of subpicture,max_subpics_minus1, in the current CVS may be signaled in a high-levelsyntax structure, e.g. VPS, DPS, SPS, PPS, APS or SEI message.

In embodiments, referring to FIG. 20 , the subpicture identifier,sub_pic_id[i], for the i-th subpicture may be signaled, when the numberof subpictures is greater than 1 (max_subpics_minus1>0).

In embodiments, one or more syntax elements indicating the subpictureidentifier belonging to each layer of each output layer set may besignaled in VPS. Referring to FIG. 20 , the sub_pic_id_layer[i][j][k],which indicates the k-th subpicture present in the j-th layer of thei-th output layer set. With this information, a decoder may recognizewhich sub-picture may be decoded and outputted for each layer of aspecific output layer set.

In embodiments, picture header (PH) may be a syntax structure containingsyntax elements that apply to all slices of a coded picture. A pictureunit (PU) may be a set of NAL units that are associated with each otheraccording to a specified classification rule, are consecutive indecoding order, and contain exactly one coded picture. A PU may containa picture header (PH) and one or more video coding layer (VCL) NAL unitscomposing a coded picture.

In embodiments, adaptation parameter set (APS) may be a syntax structurecontaining syntax elements that may apply to zero or more slices asdetermined by zero or more syntax elements found in slice headers.

In embodiments, adaptation_parameter_set_id signaled (for example asu(5)) in APS may provide an identifier for the APS for reference byother syntax elements. When ps_params_type is equal to ALF_APS orSCALING_APS, the value of adaptation_parameter_set_id may be in therange of 0 to 7, inclusive. When aps_params_type is equal to LMCS_APS,the value of adaptation_parameter_set_id may be in the range of 0 to 3,inclusive.

In embodiments, adaptation_parameter_set_id signaled as ue(v) in APS mayprovide an identifier for the APS for reference by other syntaxelements. When ps_params_type is equal to ALF_APS or SCALING_APS, thevalue of adaptation_parameter_set_id may be in the range of 0 to 7*(themax number of layers in the current CVS), inclusive. Whenaps_params_type is equal to LMCS_APS, the value ofadaptation_parameter_set_id may be in the range of 0 to 3*(the maxnumber of layers in the current CVS), inclusive.

In embodiments, each APS (RBSP) may be available to the decoding processprior to it being referenced, included in at least one AU with temporalidentifier (e.g., TemporalId) less than or equal to the temporalidentifier (e.g., TemporalId) of the coded slice NAL unit that refersit + or provided through external means. When the APS NAL unit isincluded in an AU, the value of temporal identifier (e.g., TemporalId)of the APS NAL unit may be equal to the value of the temporal identifier(e.g., TemporalId) of the AU including the APS NAL unit.

In embodiments, each APS (RBSP) may be available to the decoding processprior to it being referenced, included in at least one AU with temporalidentifier (e.g., TemporalId) equal to 0 or provided through externalmeans. When the APS NAL unit is included in an AU, the value of temporalidentifier (e.g., TemporalId) of the APS NAL unit may be equal to 0.

In embodiments, an APS (RBSP) may be available to the decoding processprior to it being referenced, included in at least one AU with temporalidentifier (e.g., TemporalId) equal to the temporal identifier (e.g.,TemporalId) of the APS NAL unit in the CVS, which contains one or morePHs or one or more coded slice NAL units referring to the APS, orprovided through external means.

In embodiments, an APS (RBSP) may be available to the decoding processprior to it being referenced, included in at least one AU with temporalidentifier (e.g., TemporalId) equal 0 in the CVS, which contains one ormore PHs or one or more coded slice NAL units referring to the APS, orprovided through external means.

In embodiments, when a flag, no_temporal_sublayer_switching_flag issignaled in a DPS, VPS, SPS or PPS, the temporal identifier (e.g.,TemporalId) value of an APS referring to the parameter set containingthe flag equal to 1 may be equal to 0, while the temporal identifier(e.g., TemporalId) value of an APS referring to the parameter setcontaining the flag equal to 1 may be equal to or greater than thetemporal identifier (e.g., TemporalId) value of the parameter set.

In embodiments, each APS (RBSP) may be available to the decoding processprior to it being referenced, included in at least one AU with temporalidentifier (e.g., TemporalId) less than or equal to the temporalidentifier (e.g., TemporalId) of the coded slice NAL unit (or PH NALunit) that refers it or provided through external means. When the APSNAL unit is included in an AU prior to the AU containing the coded sliceNAL unit referring to the APS, a VCL NAL unit enabling a temporalup-layer switching or a VCL NAL unit with nal_unit_type equal toSTSA_NUT, which indicates that the picture in the VCL NAL unit may be astep-wise temporal sublayer access (STSA) picture, may not be presentsubsequent to the APS NAL unit and prior to the coded slice NAL unitreferring to the APS. FIG. 21 shows an example on this constraint.

In embodiments, the APS NAL unit and the coded slice NAL unit (and itsPH NAL unit) referring to the APS may be included in the same AU.

In embodiments, the APS NAL unit and the STSA NAL unit may be includedin the same AU, which may be prior to the coded slice NAL unit (and itsPH NAL unit) referring to the APS.

In embodiments, the STSA NAL unit, the APS NAL unit and the coded sliceNAL unit (and its PH NAL unit) referring to the APS may be present inthe same AU.

In embodiments, the temporal identifier (e.g., TemporalId) value of theVCL NAL unit containing an APS may be equal to the temporal identifier(e.g., TemporalId) value of the prior STSA NAL unit.

In embodiments, the picture order count (POC) value of the APS NAL unitmay be equal to or greater than the POC value of the STSA NAL unit. InFIG. 21 , the value of POC M of the APS may be equal to or greater thanthe value of POC L of the STSA NAL unit.

In embodiments, the picture order count (POC) value of the coded sliceor PH NAL unit, which refers to the APS NAL unit, may be equal to orgreater than the POC value of the referenced APS NAL unit. In FIG. 21 ,the value of POC M of the VCL NAL unit referring to the APS may be equalto or greater than the value of POC L of the APS NAL unit.

In an embodiment, an APS (RBSP) may be available to the decoding processprior to it being referenced by one or more PHs or one or more codedslice NAL units, included in at least one PU with nuh_layer_id equal tothe lowest nuh_layer_id value of the coded slice NAL units that refer tothe APS NAL unit in the CVS, which contains one or more PHs or one ormore coded slice NAL units referring to the APS, or provided throughexternal means.

In an embodiment, an APS (RBSP) may be available to the decoding processprior to it being referenced by one or more PHs or one or more codedslice NAL units, included in at least one PU with TemporalId equal tothe TemporalId of the APS NAL unit and nuh_layer_id equal to the lowestnuh_layer_id value of the coded slice NAL units that refer to the APSNAL unit in the CVS, which contains one or more PHs or one or more codedslice NAL units referring to the PPS, or provided through externalmeans.

In an embodiment, an APS (RBSP) may be available to the decoding processprior to it being referenced by one or more PHs or one or more codedslice NAL units, included in at least one PU with TemporalId equal to 0and nuh_layer_id equal to the lowest nuh_layer_id value of the codedslice NAL units that refer to the APS NAL unit in the CVS, whichcontains one or more PHs or one or more coded slice NAL units referringto the PPS, or provided through external means.

In an embodiment, an APS (RBSP) may be available to the decoding processprior to it being referenced by one or more PHs or one or more codedslice NAL units, included in at least one PU with TemporalId equal to 0and nuh_layer_id equal to the lowest nuh_layer_id value of the codedslice NAL units that refer to the APS NAL unit in the CVS, whichcontains one or more PHs or one or more coded slice NAL units referringto the PPS, or provided through external means.

In embodiments, All APS NAL units with a particular value ofadaptation_parameter_set_id and a particular value of aps_params_typewithin a PU, regardless of whether they are prefix or suffix APS NALunits, may have the same content.

In embodiments, regardless of the nuh_layer_id values, APS NAL units mayshare the same value spaces of adaptation_parameter_set_id andaps_params_type.

In embodiments, the nuh_layer_id value of an APS NAL unit may be equalto the lowest nuh_layer_id value of the coded slice NAL units that referto the NAL unit that refer to the APS NAL unit.

In an embodiment, when an APS with nuh_layer_id equal to m is referredto by one or more coded slice NAL units with nuh_layer_id equal to n.the layer with nuh_layer_id equal to m may be the same as the layer withnuh_layer_id equal to n or a (direct or indirect) reference layer of thelayer with nuh_layer_id equal to m.

FIG. 22 is a flowchart is an example process 2200 for decoding anencoded video bitstream. In some implementations, one or more processblocks of FIG. 22 may be performed by decoder 210. In someimplementations, one or more process blocks of FIG. 22 may be performedby another device or a group of devices separate from or includingdecoder 210, such as encoder 203.

As shown in FIG. 22 , process 2200 may include obtaining from an encodedvideo bitstream a coded video sequence including a picture unitcorresponding to a coded picture (block 2210).

As further shown in FIG. 22 , process 2200 may include obtaining a PHNAL unit included in the picture unit (block 2220).

As further shown in FIG. 22 , process 2200 may include obtaining atleast one VCL NAL unit included in the picture unit (block 2230).

As further shown in FIG. 22 , process 2200 may include decoding thecoded picture based on the PH NAL unit, the at least one VCL NAL unit,and an adaptation parameter set (APS) included in an APS NAL unitobtained from the coded video sequence, wherein the APS NAL unit isavailable to the at least one processor before the at least one VCL NALunit (block 2240).

As further shown in FIG. 22 , process 2200 may include outputting thedecoded picture (block 2250).

In embodiments, the APS NAL unit is available to the decoding processprior to being referenced by one or more picture headers (PHs) or one ormore coded slice network abstraction layer (NAL) units, included in atleast one prediction unit (PU) with nuh_layer_id being equal to thelowest nuh_layer_id value of the more or more coded slice NAL units thatrefer to the APS NAL unit in the CVS, which contains the one or more PHsor the one or more coded slice NAL units referring to the APS.

In embodiments, a temporal identifier of the at least one VCL NAL unitis greater than or equal to a temporal identifier of the APS NAL unit.

In embodiments, the temporal identifier of the APS NAL unit may be equalto zero.

In embodiments, a POC of the at least one VCL NAL unit may be greaterthan or equal to a POC of the APS NAL unit.

In embodiments, a layer identifier of the PH NAL unit and a layeridentifier of the at least one VCL NAL unit are greater than or equal toa layer identifier of the APS NAL unit.

In embodiments, the PH NAL unit, the at least one VCL NAL unit, and theAPS NAL unit are included in a single access unit

In embodiments, the coded video sequence further includes an STSA NALunit corresponding to an STSA picture, and the STSA NAL unit is notlocated between the APS NAL unit and the at least one VCL NAL unit.

In embodiments, the at least one VCL NAL unit, the APS NAL unit, and theSTSA NAL unit may be included in a single access unit.

In embodiments, the temporal identifier of the APS NAL unit may begreater than or equal to a temporal identifier of the STSA NAL unit.

In embodiments, a picture order count (POC) of the APS NAL unit may begreater than or equal to a POC of the STSA NAL unit.

Although FIG. 22 shows example blocks of process 2200, in someimplementations, process 2200 may include additional blocks, fewerblocks, different blocks, or differently arranged blocks than thosedepicted in FIG. 22 Additionally, or alternatively, two or more of theblocks of process 2200 may be performed in parallel.

Further, the proposed methods may be implemented by processing circuitry(e.g., one or more processors or one or more integrated circuits). Inone example, the one or more processors execute a program that is storedin a non-transitory computer-readable medium to perform one or more ofthe proposed methods.

The techniques described above can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 23 shows a computersystem 2300 suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by computer central processing units (CPUs),Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 23 for computer system 2300 are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system 2300.

Computer system 2300 may include certain human interface input devices.Such a human interface input device may be responsive to input by one ormore human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard 2301, mouse 2302, trackpad 2303, touch screen2310 and associated graphics adapter 2350, data-glove, joystick 2305,microphone 2306, scanner 2307, camera 2308.

Computer system 2300 may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen 2310, data-glove, or joystick 2305, but there can also betactile feedback devices that do not serve as input devices), audiooutput devices (such as: speakers 2309, headphones (not depicted)),visual output devices (such as screens 2310 to include cathode ray tube(CRT) screens, liquid-crystal display (LCD) screens, plasma screens,organic light-emitting diode (OLED) screens, each with or withouttouch-screen input capability, each with or without tactile feedbackcapability—some of which may be capable to output two dimensional visualoutput or more than three dimensional output through means such asstereographic output; virtual-reality glasses (not depicted),holographic displays and smoke tanks (not depicted)), and printers (notdepicted).

Computer system 2300 can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW2320 with CD/DVD or the like media 2321, thumb-drive 2322, removablehard drive or solid state drive 2323, legacy magnetic media such as tapeand floppy disc (not depicted), specialized ROM/ASIC/PLD based devicessuch as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system 2300 can also include interface(s) to one or morecommunication networks (955). Networks can for example be wireless,wireline, optical. Networks can further be local, wide-area,metropolitan, vehicular and industrial, real-time, delay-tolerant, andso on. Examples of networks include local area networks such asEthernet, wireless LANs, cellular networks to include global systems formobile communications (GSM), third generation (3G), fourth generation(4G), fifth generation (5G), Long-Term Evolution (LTE), and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters (954) that attached to certain generalpurpose data ports or peripheral buses (949) (such as, for exampleuniversal serial bus (USB) ports of the computer system 2300; others arecommonly integrated into the core of the computer system 2300 byattachment to a system bus as described below (for example Ethernetinterface into a PC computer system or cellular network interface into asmartphone computer system). As an example, network 2355 may beconnected to peripheral bus 2349 using network interface 2354. Using anyof these networks, computer system 2300 can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces (954) as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core 2340 of thecomputer system 2300.

The core 2340 can include one or more Central Processing Units (CPU)2341, Graphics Processing Units (GPU) 2342, specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)2343, hardware accelerators 2344 for certain tasks, and so forth. Thesedevices, along with Read-only memory (ROM) 2345, Random-access memory(RAM) 2346, internal mass storage such as internal non-user accessiblehard drives, solid-state drives (SSDs), and the like 2347, may beconnected through a system bus 2348. In some computer systems, thesystem bus 2348 can be accessible in the form of one or more physicalplugs to enable extensions by additional CPUs, GPU, and the like. Theperipheral devices can be attached either directly to the core's systembus 2348, or through a peripheral bus 2349. Architectures for aperipheral bus include peripheral component interconnect (PCI), USB, andthe like.

CPUs 2341, GPUs 2342, FPGAs 2343, and accelerators 2344 can executecertain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM2345 or RAM 2346. Transitional data can be also be stored in RAM 2346,whereas permanent data can be stored for example, in the internal massstorage 2347. Fast storage and retrieve to any of the memory devices canbe enabled through the use of cache memory, that can be closelyassociated with one or more CPU 2341, GPU 2342, mass storage 2347, ROM2345, RAM 2346, and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not byway of limitation, the computer system havingarchitecture 2300, and specifically the core 2340 can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core 2340 that are of non-transitorynature, such as core-internal mass storage 2347 or ROM 2345. Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core 2340. A computer-readablemedium can include one or more memory devices or chips, according toparticular needs. The software can cause the core 2340 and specificallythe processors therein (including CPU, GPU, FPGA, and the like) toexecute particular processes or particular parts of particular processesdescribed herein, including defining data structures stored in RAM 2346and modifying such data structures according to the processes defined bythe software. In addition or as an alternative, the computer system canprovide functionality as a result of logic hardwired or otherwiseembodied in a circuit (for example: accelerator 2344), which can operatein place of or together with software to execute particular processes orparticular parts of particular processes described herein. Reference tosoftware can encompass logic, and vice versa, where appropriate.Reference to a computer-readable media can encompass a circuit (such asan integrated circuit (IC)) storing software for execution, a circuitembodying logic for execution, or both, where appropriate. The presentdisclosure encompasses any suitable combination of hardware andsoftware.

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method of generating an encoded video bitstreamusing at least one processor, the method comprising: obtaining videodata corresponding to a picture unit; generating a picture header (PH)network abstraction layer (NAL) unit corresponding to the picture unit;generating at least one video coding layer (VCL) NAL unit correspondingto the picture unit; generating a coded video sequence (CVS) based onthe PH NAL unit, the at least one VCL NAL unit, and an adaptationparameter set (APS) included in an APS NAL unit; and outputting theencoded video bitstream including the coded video sequence, wherein theAPS NAL unit is included in at least one prediction unit (PU) having anuh_layer_id value that is equal to a lowest nuh_layer_id value of themore or more coded slice NAL units that refer to the APS NAL unit. 2.The method of claim 1, wherein the APS NAL unit is available to the atleast one processor before at least one video coding layer (VCL) NALunit included in the picture unit, and wherein the APS NAL unit isavailable to a decoder of the encoded video bitstream prior to beingreferenced by one or more picture headers (PHs) or one or more codedslice NAL units included in the CVS.
 3. The method of claim 1, wherein atemporal identifier of the at least one VCL NAL unit is greater than orequal to a temporal identifier of the APS NAL unit.
 4. The method ofclaim 1, wherein a picture order count (POC) of the at least one VCL NALunit is greater than or equal to a POC of the APS NAL unit.
 5. Themethod of claim 1, wherein a layer identifier of the PH NAL unit and alayer identifier of the at least one VCL NAL unit are greater than orequal to a layer identifier of the APS NAL unit.
 6. The method of claim1, wherein the CVS further comprises a step-wise temporal sublayeraccess (STSA) NAL unit corresponding to an STSA picture, and wherein theSTSA NAL unit is not located between the APS NAL unit and the at leastone VCL NAL unit.
 7. The method of claim 6, wherein the PH NAL unit, theat least one VCL NAL unit, the APS NAL unit, and the STSA NAL unit areincluded in a single access unit.
 8. The method of claim 6, wherein atemporal identifier of the APS NAL unit is greater than or equal to atemporal identifier of the STSA NAL unit.
 9. The method of claim 6,wherein a picture order count (POC) of the APS NAL unit is greater thanor equal to a POC of the STSA NAL unit.
 10. A device for generating anencoded video bitstream, the device comprising: at least one memoryconfigured to store program code; and at least one processor configuredto read the program code and operate as instructed by the program code,the program code including: first obtaining code configured to cause theat least one processor to obtain video data corresponding to a pictureunit; first generating code configured to cause the at least oneprocessor to generate a picture header (PH) network abstraction layer(NAL) unit included in the picture unit; second generating codeconfigured to cause the at least one processor to generate at least onevideo coding layer (VCL) NAL unit corresponding to the picture unit;third generating code configured to cause the at least one processor togenerate a coded video sequence (CVS) based on the PH NAL unit, the atleast one VCL NAL unit, and an adaptation parameter set (APS) includedin an APS NAL unit; and output code configured to cause the at least oneprocessor to output the encoded video bitstream including the codedvideo sequence, wherein the APS NAL unit is included in at least oneprediction unit (PU) having a nuh_layer_id value that is equal to alowest nuh_layer_id value of the more or more coded slice NAL units thatrefer to the APS NAL unit.
 11. The device of claim 10, wherein the APSNAL unit is available to a decoder of the encoded video bitstream beforethe at least one VCL NAL unit, and wherein the APS NAL unit is availableto the decoder of the encoded video bitstream prior to being referencedby one or more picture headers (PHs) or one or more coded slice NALunits included in the CVS
 12. The device of claim 10, wherein a temporalidentifier of the at least one VCL NAL unit is greater than or equal toa temporal identifier of the APS NAL unit.
 13. The device of claim 10,wherein a picture order count (POC) of the at least one VCL NAL unit isgreater than or equal to a POC of the APS NAL unit.
 14. The device ofclaim 10, wherein a layer identifier of the PH NAL unit and a layeridentifier of the at least one VCL NAL unit are greater than or equal toa layer identifier of the APS NAL unit.
 15. The device of claim 10,wherein the coded video sequence further comprises a step-wise temporalsublayer access (STSA) NAL unit corresponding to an STSA picture, andwherein the STSA NAL unit is not located between the APS NAL unit andthe at least one VCL NAL unit.
 16. The device of claim 15, wherein thePH NAL unit, the at least one VCL NAL unit, the APS NAL unit, and theSTSA NAL unit are included in a single access unit.
 17. The device ofclaim 15, wherein a temporal identifier of the APS NAL unit is greaterthan or equal to a temporal identifier of the STSA NAL unit.
 18. Thedevice of claim 15, wherein a picture order count (POC) of the APS NALunit is greater than or equal to a POC of the STSA NAL unit.
 19. Anon-transitory computer-readable medium storing instructions, theinstructions comprising: one or more instructions that, when executed byone or more processors of a device for generating an encoded videobitstream, cause the one or more processors to: obtain video datacorresponding to a picture unit; generate a picture header (PH) networkabstraction layer (NAL) unit corresponding to the picture unit; generateat least one video coding layer (VCL) NAL unit corresponding to thepicture unit; generate a coded video sequence (CVS) based on the PH NALunit, the at least one VCL NAL unit, and an adaptation parameter set(APS) included in an APS NAL unit; and output the encoded videobitstream including the coded video sequence, wherein the APS NAL unitis included in at least one prediction unit (PU) having a nuh_layer_idvalue that is equal to a lowest nuh_layer_id value of the more or morecoded slice NAL units that refer to the APS NAL unit.
 20. Thenon-transitory computer-readable medium of claim 19, wherein the APS NALunit is available to a decoder of the encoded video bitstream before theat least one VCL NAL unit, and wherein the APS NAL unit is available tothe decoder of the encoded video bitstream prior to being referenced byone or more picture headers (PHs) or one or more coded slice NAL unitsincluded in the CVS.